The goal of this project is to develop high-level physiological control, improve low-level dynamic piston control, and develop hemodynamic sensing capabilities for the pediatric TORVADTM, a unique ventricular assist system that delivers low-shear, synchronous, pulsatile flow, using controlled piston motion within a torus-shaped pumping chamber. The pediatric TORVAD is intended for patients with a body surface area from 0.6 to 1.5 m2, but the design can be scaled to adapt to a wide variety of patient sizes and needs. Low shear in the pumped blood is managed by the relatively low speed of the pistons which are supported by hydrodynamic bearings that maintain a fixed piston-torus gap. The primary operating mode delivers a 15 mL counterpulse ejection, but the pump can also operate asynchronously to deliver full cardiac support up to 4 L/min. The system synchronizes with the heart to preserve aortic valve flow and maintains autoregulation of cardiac output by the Frank-Starling mechanism. The design of the TORVAD also enables determination of differential pump pressure, without additional sensors. This inherent sensing capability can be used to inform patient medications and optimal pump support. These device advantages have been confirmed in benchtop studies and acute and chronic animal experiments with an adult TORVAD, and results have indicated preservation of high-molecular-weight von Willebrand Factor. The pediatric TORVAD has been designed to exhibit these same advantages, and thus has the potential to reduce bleeding, thrombus formation, and strokes that are associated with the use of other pediatric ventricular assist devices. Specific aims for Phase I are: (1) Improve the dynamic piston control; (2) Implement dynamic pressure sensing during pump actuation; and (3) Develop systemic vascular resistance (SVR) estimation. Specific aims for Phase II are: (1) Implement physiologic control of VAD flow; (2) Fabricate devices for acute and chronic animal experiments; (3) Perform four acute animal studies to assess control algorithms, pressure signal sensing, and SVR estimation; (4) Perform six chronic animal studies to assess long-term viability of the pediatric TORVAD and algorithms.